Substitute unit for circuit testing and grounding



June 10, 1952 H. KRIDA 2,600,304

SUBSTITUTE UNIT FOR CIRCUIT TESTING ANDGROUNDING Filed June 10, 1950 2 SHEETSSHEET 1 inventor: Hugh Krida,

June 10, 1952 SUBSTITUTE UNIT FOR CIRCUIT TESTING AND GROUNDING 2 SHEETS-SHEET 2 Filed June 10, 1950 Irwventor Hugh KP Ida His Attorney Patented June 10, 1952 SUBSTITUTE UNIT FOR CIRCUIT TESTING AND GROUNDING Hugh Krida, Upper Darby, 2a., :assignor'to General Electric Company, a corporation of New .York

Application June 10, 1950, SerialrNo. 167,326

.13 Claims. 1

The invention relates'to electrical circuittesting and grounding apparatus, particularly "of a unit type "suitable 'for substitution for a me'talclad circuitbreaker unit-ina high voltage-polyphase power system wherein 'buses, feeder lines, tie lines, transformers, generators and'other apparatus are interconnected and protected by means of the circuit breaker units, "each having the usual disconnect contacts that separate coincidental to 'removalpf'theunit from its stationary'cubicle.

The principal object is to provide "a selective circuit testing and grounding 'unit that may temporarily be substituted "for "any circuit breaker unit in such system so' that "both of the circuits normally interconnectedby the 'circuit breaker unit'maybe readily tested foriascertaininga line ordeadcircuit condition and'either circuit as "selected may be grounded to insure "the'safety'of servicemenworkingthereon.

Another'object is to provide safely insulated and readily "accessible contact receptacles in the substitute unit for connectingan externalsource of'test'voltage or asuitable type of external testing deviceto either "or both'circuits in orderto perform "testing'functions of the following nature: (1) selectively checking the presence *or absence of voltage on "eachpolyphase incoming bus or outgoing'line'conductor; (2) checking the relative phase "sequence of the "bus and line circuits'or the actual; phase sequence 'of each; (3) applying a test voltage to any bus orjline conductor for the purpose "of checkingthe insulation resistance'thereof; "and (4) connecting a'resistance measuring device to any bus .or line conductor to measure the resistance of afau'lt thereon in order to determineits approximate'location.

Another object is to render the improved selective circuit testing and grounding substitute unit mechanically -interchangeable with the metalclad circuit breaker'unit and" capable of utilizing the vertical'lift'mechanism and disconnect contactsj'provided therefor .inthe metal-clad en:-

vclosure to insure the same safety to operating personnel during grounding .or testing operations as'is provided by the-enclosed switchgear during normal operation.

Another objectis to enablethe improved substitute unit to short circuit andsimultaneously ground either the three incoming polyphase bus conductorsor the threeoutgoin polyphase line conductors without the need of any external cable connections so thatthe doorofthemetalclad compartment can be closed and locked for absolute safety with the improved; grounding tes in unit replacing the circuit breaker unit therein and iwithalltparts ofthegimproved un it capable of withstandingfullshort circuit; stresses Without damage if the unit should be applied to a live circuit.

Another obeot is to enable the imnro d $111 1 to perform with :a snap actionits selectrv circuiting and grounding functions 11 W electrical eontrolin case electriccontrolpoweris a ailableas well toprcvide ior m nua emote control of :the short circuitirl and gi l l'ltiilig functions even wheiiaelectriccontro power-lana available.

.Another object is to provide adequate timechanical "and electrical interlockin .fpr the mproved selective circuit testing andgroun unite-so .as v to insure the maximum safet or 9D- eratingpersonnel Furth r obj cts and advanta es of the m cntion will appear in. t e following descriptionef the accompanying drawing in which Fig. i l is a perspective view of the improved 'selectivescirc t testing and groundinesubstitute unit read; ,1' elevating into the connected operating position inside the metal enclosing -.c,u'bicle from which the :normally housed polyphase high viqllzaefi power circuit breaker has been temporarily removed. .Fig. 2 is a schematic perspective ex ploded view. showing the:essential-operating elee ments ofthe unit, and. Fig. -3c-shows an improved double-prong testinghot stick;adapted foruse with the improved unit.

As shown'in Fig. '1, the improved selective sire cuit testing; and, grounding substitute unit indicated gencrallyby the reference character :tfl-is mounted on a-:tru.ck H provided with lsuitable rollers'l2 so that the unit In may bereadil-y rolled into :any desired metalecla'd cubicle compartment l3. as a temporarysubstitute for a high voltage power circuit breaker unit of=the disconnectably removable type. Thus the metal-clad cubicle I 3 isshown provided with a polyphase series of disconnect receptacles or sockets MA, MB and MC that-are electrically conncted-as indicated -schematically in the draw'lng'to' the corresponding" line conductors VA,"'B-and C as well as'a corresponding polyphase serie -of disconnect receptacles, orsockets" 15a, l'5b; |5CfOI1C- trical connection tothe bus conductors ,a, b and c. Itwill be understood that the power circuit breaker unit norma ly ous d w th n t me a clad cubicle I3 serves to c nne .or disc nnect thelinelconduc ors with the busc n uctors, and

may be provided with suitable automat c controls for affording conventional protection to the lines. In order to cooperate in providing a positive low-resistance ground path for the improved testing and grounding unit of the present invention, the metal-clad cubicle I3 is provided with a special grounding contact shoe [8 that is connected with the permanently grounded cubicle structure as indicated.

The improved testing and grounding unit 10 has the two juxtaposed polyphase series of bushing insulated connection plugs A, 20B, 20C and 2la, H1), H0 projecting in alignment upwardly therefrom for engagement respectively with the corresponding polyphase series of line and bus connection receptacles or sockets Ma, 14b, He and I511, 151), 150 when the safety unit In is raised into its operating position inside the cubicle l3 by means of the usual circuit breaker lifting mechanism 23 engaging with the ledges 24 provided on opposite sides of the unit l0. During I such elevation, the elongated ground connector 22 of the unit electrically contacts the grounding shoe [6 of the cubicle so as to set up an adequate ground path in the event that either the line conductors or the bus conductors are to be selectively grounded by the selective grounding switch mechanism within the unit [0 in the manner explained more in detail hereinafter.

As indicated in Fig. 1, the unit H3 is provided with a lower series of three bus test plug receptacles 25a, 25b and 25c as well as an upper series of three line test plug receptacles 26A, 26B, 26C disposed in predetermined equally spaced apart alignment and each of which (although only one is actually shown) is separately interconnected by means of a suitable insulated cable conductor 21 with its corresponding one of the main connection plugs 20A, B and C and 2 la, b and 0. Thus, these two series of readily accessible test plug receptacles enable the necessary testing of the bus and line conductors, either singly or jointly, to be accomplished conveniently and safely. Thus, an improved glow tube type high voltage detector constructed like a double-prong fork as shown in Fig. 3 may be used to detect selectively the voltage condition across any adjacent pair of bus and line conductors. A single rod-like device is commonly known as a hot stick. In the present instance, the test device is shown as comprising a crosshead in the form of an electrostatic glow tube 28 having the projecting terminal plugs or prongs 2 8 and an insulating handle 9. The projecting terminal plugs or prongs 28' are suitably spaced the same distance as that separating the adjacent receptacles to permit simultaneously contacting any two adjacent test receptacles for checking voltage differences across corresponding phase conductors to determine whether the relative phase sequence and the phasing of the two circuits are correct. As shown, one of the two terminal plugs 28" is constructed so as to be separately rotatable about the cross-head portion as indicated so that it can be turned to a non-operative position so that the device then becomes a single hot stick for contacting any single conductor with the remaining fixed terminal plug so as to determine the presence or absence of voltage on any conductor preliminary to grounding the circuit. Furthermore, insulated cables having terminal plugs which fit into the test receptacles may be used as temporary connections to either the bus or line conductors for applying test voltages thereto or for servin as connections therefrom to resistance measuring equipment suitable for determining the proximity of faults or to external checking or testing apparatus containing potential transformers with required secondary devices for checking voltage, phase sequence, etc. as may be desired. For protectively shielding the test receptacles 25a, 2) and c or 26A, B and C when they are not being used, a hinged cover It) is provided and arranged for lockin in the closed position as shown, thus effectively blocking access to the test receptacles except during an intentional testing operation.

As indicated in Fig. 2, each of the bushing insulated connection plugs 20A, 20B, 20C (line), and 2m, Hi) and 210 (bus) projecting in predetermined spaced apart alignment from the unit l0 carries at its inner end in conducting relation therewith a corresponding one of the stationary switch contacts 30A, 30B and 300 (line) and 3la, 3lb and 310 (bus) which are thus mounted in predetermined spaced apart alignment. A series of intermediate stationary switch contacts 32a, 32b and 320 are separately mounted in corresponding spaced apart alignment inside unit It), and each intermediate contact has connected in conducting relation therewith a corresponding one of the jointly movable switch members 33a, 33b and 330 for selective engagement with either of a corresponding pair of the connection plug mounted stationary switch contacts. As shown, the movable switch member 33a is pivotally mounted directly on the intermediate switch contacts 32a, b, 0, respectively, and the spacing is such that blades 33a, b and c can engage with either of the pair of stationary switch contacts 30A or 3 la dependin upon the position to which the switch member 33a is selectively operated. Each of the other jointly movable selective switch members 3311 and 330 is mounted to operate in a similar manner.

The movable switch member 33a is selectively operated between its two circuit-closing positions by means of the pivotally connected insulation link 34a that is connected by the yoke 35a to be moved by the clevis 36a fixed to the operating shaft 37. Each of the other selective switch members 33b and 330 is similarly connected to be jointly operated with the selective switch member 33a upon rotation of the operating shaft 31. As shown, shaft 37 is rotated by means of the removable manual operating handle 38 provided with the pin 39 for engaging with the slotted end 40 of the operating shaft. As shown in Fig. l, a double key shaped opening 4| is provided in the side of the enclosing casing of the unit In for interlocking engagement with the projecting end of the pin 39 so that the manual selective switch operating handle 38 can be removed only after the joint operation of the selective gang operated switch members 33a, 33b and 330 to either circuit closing position is completed.

For positively and instantaneously grounding either the three-phase bus or the three-phase line, whichever has been selected, a series of grounding switch resilient contacts a, 50b and 500 are pivotall mounted on the switch members 5|a, Fill) and 510 that in turn are pivotally mounted in conducting relation on the hinge blocks 52a, 52b and 52c which may be brazed on the common ground bus 53. As shown in Fig. 1, bus 53 is connected to the external ground connector 22 thereby constituting a direct lowresistance ground path via fixed shoe Hi. The ground switch members 5Ia, 51b and 5lc are interconnected for joint operation by the common operating bar 54 on which the pair of links 55 are pivoted for operation by the clevis arms 56 that are pinned or otherwise fixed to their common operating shaft 51. This "grounding switch operating "shaft 57 is normally biased to operate the grounding switch contacts 50a, 50b and 50c to the open position by means of a plurality of biasing springs 60 connected through the links 6! with the double-armed actuating crank 62 that is fixedly pinned tothe shaft 51 The grounding switch contacts 50a, 50b and toe preferably are closed with a snap action by means of a spring 'charge'cl mechanism '80 and a compound toggle mechanism com rising the link 63 that is pivotally supported between the arms of the crank "62 an is pivotauy intercom nected with one end of the bell "crank member '64 that is pivotally mounted on the fixed shaft 65. The other end of the bell "crank is connected to the tog le links 66 which in turn are connected bypin 61 and the toggle links L68 with the U-shaped guide link 69 that is pivotally mounted on the fixed shaft 12. A latch roller 13 carried between the ends of the toggle links 68 is engaged by a latch 14 mounted on the laterally extending trip shaft 75 and biased by spring 15 into a position to engage with the latch roller 13. An interlock pawl 1'! isc'arried on the righthand end of the trip shaft 15. The latch 14 may be released or tripped by the plunger 18' of the tripping 'electromagnet '18 upon energi'zation thereof, and the tripping of latch 14 ehables the blasing'springs 60 to operate the three groon'm ing switch contacts 56a, 50band 5m: to the open position with a snap action upon the resulting collapse of the compound toggle mechanism.

A spring-charged mechanisrmfindicated generally by the reference character fifljmay be pro-- video. for operating the compound trip-free toggle mechanism with a snap action to close the grounding switch contacts sea, v 59b and 5llc when the latch 14 engages with the latch roller 13 "although it will be understood that other forms of snap action closing mechanisms may be used if desired: For providing the c1osiz1gthiust,'the spring-charged mechanism 80 is provided with a pair of energy-accumulating springs 8| that are compressible between the hired support 82 and the movable channel-sectioned cross head as although on y the far side spring is shown in order more clearly to "reveal other details "or construction. The movable cross head 83, sultably guided for reciprocal vertical movement, is operatively connected by a pair of eccentric followers 84 for the eccentrics 85 which are 'fixed to the opposite ends of the heavy 'fiywheel 86 which is mounted for rotation on the Shaft 81 havings'uitable fixed bearings (not shown). Ac-

cordingly, any reciprocating movement of the cross head is accompanied by corresponding rotation of the fiywheel'BS and vice've'rsa. The fiywheel 86 preferably is provided'with a peripheral groove 90 within which a roller chain is located and fixedly secured to the flywheel.

A manually operable ratchet mechanism 9! is provided with a pawl 92 for successively enrotate flywheel 86- in the-clockwisedlrection, but

the releasable latch 94 engages with a notch?! formed in "the periphery of the flywheel 86 and thereby latches the spring-charged mechanism against the further release of the ener gy stored in the springs 8|. The cross head 83 carries an operating plunger 91 for e'ngagingwith the knee of the toggle formed by the links '66 and 68 so as to extend this toggle while the latch 14 engages with the latch roller 13 and thereby move the arm 64 to operate thr'oughllnk 63 to rotatetheclevis member 62 and shaft 51 to quick- 1y close the grounding switch contacts 50a, 50b and 56c upon release of the latch 94 and resulting-r'elease of the energy stored inthe Springs B-I. The toggle mechanism is latched in the closed position in'whioh it is shown by the engagement of the "double latch 88 w-iththe ends of pin 89 at the'k'nee'of the toggle.

As shown in Fig. 2, provision is made for releasing the latched to close the grounding switch contacts with a snap action either by-ene'rglzln'g the releasing electromagnet I00 or manually operating the releasing-arm 191. in either case. thec'ollar 32 engages with the bifurcated end of the latch 94 to eifect the quick release of the energy stored in the springs 8|. I'he releasing electromagnet I00 is arranged to be energized through a circuit controlled by the manually operable selector switch 35 which is connected to "a plug receptacle I06 mounted on the front of the unit H: as shown in'Fig. 1 "and arranged to be connected to a suitable source of power by a cable It! provided with the two separately operable push button switches it for remote electrical control. When the selector switch m5 is moved from the position in which it is shown mote operation is desired. A suitable indicator H1 is ro'tatably mounted on shaft 3! and corrnected by the rod 1 IS with the movable groundingswitch member SI'a so as to indicate whether the grounding switch is opened or closed from the front of the unit it as indicated in Fig. 1. Also, transparent side panels 1T9 are provided for facilitating inspection and checking of the selector and grounding switch mechanism mounted inside the unit I0.

Interlocking mechanism is provided for insuring the maximum safety in the operation of the improved testing'and groundingunit it. As previouslypointed out, the selector switches 33a, 33b and 330 necessarily must be completely operated into a selected circuit closing position before the manual selector switch operating'handle38 can be removed, and this handle necessarily must be removed before the unit It can be rolled into the "cubicle l3 and operated by the elevating mechanism 23 into the connected position. This serves in effect as an interlock to insure that the selective switch can never "be necessarily 'must be manually charged before the unit in is inserted in the cubicle l3 and the manual spring charging handle 9| removed. Normally the grounding switch contacts 50a, 50b and 500 are in the open position when unit 10 is inserted in the cubicle 13. However, the automatic interlocking trip lever I20 is provided for engaging with the cam I2! that is fixed to the side of the cubicle 13 for insuring that the grounding switch must be in the open position before the unit in can be raised to its connected position. Thus, automatic trip lever I20 is connected by the rod i22 with the pivot arm I23 carried on the unit and having the adjustable stop I24 for engaging with the interlock pawl IT to release the trip latch 14 from the latch roller 73 and thereby collapse the compound toggle mechanism to open the grounding contacts 50a, 50b and 500. But the operation of the automatic trip lever I20 normally will produce no effect since the grounding switch contacts are normally open when unit I!) is elevated into its connected position.

With the improved unit It in its connected position inside the cubicle l3 and with the springcharged mechanism 80 charged, the latter may be released electrically in the manner previously described as long as the manual selector switch Hi remains in the position in which it is shown in Fig. 2 and a suitable source of outside power is available. source available, then the manual release handle H5 may be operated to effect the release of the spring-charged mechanism 89 to effect closing of the grounding switch contacts 50a, 59b and 500 with a snap action so as to ground the particular set of bus or line conductors which the selector switches 33a, 33b and 330 interconnect with the grounding switch intermediate stationary contacts 32a, 32b and 320 as selected before the unit was inserted in the cubicle 13.

The grounding switch may be opened with a snap action to remove the ground from the conductors by operating the selector switch W5 to its other position in which the contacts H0 are engaged so as to permit energizing the trip coil 18 from the remote push button. Thereupon, the plunger 18 releases the latch 74 thereby collapsing the compound toggle mechanism to permit the biasing spring 60 to open the grounding switch contacts with a snap action. Under these conditions, the interlocking cam ISO is rotated sufficiently to disable the manual release handle H5.

In case no suitable external source of power is available for energizing the trip coil i8, then trip lever (29 may be operated manually, thereby effecting manual release of the trip latch 14 to open the grounding switch contacts with a snap action.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A selective circuit grounding substitute unit having in combination a double throw circuit selective switch, a single throw grounding switch having biasing means for opening the switch and connections with the selective switch for grounding the circuit selected thereby, an energy accumulating spring closing mechanism having a remotely operable releasing control element for closing the grounding switch with a snap action and separately controlled latching means for holding the grounding switch closed and releasing the grounding switch for snap action opening by the biasing means.

2. A selective circuit grounding substitute unit In case there is no such power having in combination a pair of separately insulated stationary switch contacts each having means for connection with a separate circuit upon substitution of the unit, an intermediate separately insulated stationary switch contact having a movable switch member electrically interconnected therewith and provided with operating means interlocked to be effective only before and after substitution of the unit for selectively and separately connecting the intermediate contact with each of the pair of contacts, a grounded switch member engageable with the intermediate contact for grounding the same, spring means biasing the grounding switch member to the opening position, energy storing spring means for closing the grounded switch member with a snap action, latching means for holdin the grounded switch member closed, and latch tripping means for releasing the grounded switch member for snap action opening by the biasing spring means.

3. A selective circuit grounding substitute unit having in combination a pair of stationary switch contacts, each having means for connection with a separate circuit upon movement of the unit to a predetermined position, an intermediate stationary switch contact having a switch member electrically interconnected therewith and provided with interlocking means for rendering the switch member movable selectively into circuit closing engagement with either of the pair of contacts only before and after movement of the unit to the predetermined position, a reversely movable grounding switch member having means for grounding the member upon movement of the unit to the predetermined position, means biasing the grounding switch member for movement in one direction, energy storing means for effecting snap action movement of the grounding switch member in the opposite direction into engagement with the intermediate contact for grounding the same, latching means for holding the switch in engagement with the intermediate contact independently of the energy storing means, and latch tripping means for controlling the snap action disengagement of the grounding switch member from the intermediate contact in accordance with its bias,

4-. A selective circuit grounding substitute unit for plural circuit apparatus having separate circuit connection sockets and a separate grounding terminal, said unit having in combination a pair of stationary switch contacts each having means for connection with a separate circuit including a disconnect plug electrically connected with the contact for engaging a corresponding socket upon movement of the unit to a predetermined position, an intermediate stationary switch contact provided with a movable switch member and having operating means interlocked to be effective only before and after substitution of the unit for selectively and separately connecting the intermediate contact with each of the pair of contacts, a separately operable switch member having an interconnected conducting shoe for engaging the grounding terminal upon movement of the unit to the predetermined position and separately releasable remotely controlled spring biasing means for operating the separately operable switch member with a snap action into and out of circuit closing engagement with the intermediate contact.

5. A selective circuit grounding substitute unit having in combination a pair of stationary switch contacts each having means for connection with a separate circuit upon movement of the unit to a predetermined position, an intermediate stationary switch contact provided with a selectively movable switch member for selectivelyand separately connecting the intermediate contact with each of the pair of contacts, means including a grounding switch member having means for grounding the switch member upon movement of the unit to the predetermined position, releasable means efiective only for operating the grounding switch member with a snap action into engagement with the intermediate contact for grounding, the same, latching means for independently holding the grounding switch member in engagement with the intermediate contact, and. spring biasing means for operating thegrounding switch member with a snap action out of engagement with the intermediate contact upon release 01 the latching means.

6. A selective polyphase circuit grounding substitute unit having in combination a plurality of pairs of stationary switch contacts, each having means for connection with a corresponding polyphase; circuit conductor upon movement of the unit to a predetermined position, a corresponding plurality of intermediate stationary switch contacts each provided with a selectively movable switch member for separately connecting each intermediate contact with either of the corresponding pair of contacts, means for jointly moving the selective switch members to each selected connecting position only before and after movement of the unitto the predetermined position, means including a corresponding plurality of grounding switch members having common means for grounding each switch member upon movement-of the unit to the predetermined position and each engageable with a corresponding intermediate contact for grounding the same, a remotely releasable energy storing spring means for jointly operating the grounding switch members into engagement with the intermediate stationary switch contacts, latching means for indedependently holding the grounding switch members in engagement with the intermediate stationary switch contacts, and spring biasing means for operating the grounding switch members with snap action out of engagement with the intermediate stationary switch contacts upon release of the latching means.

7. A selective circuit grounding substitute unit for operation in a switchgear cubicle having separate circuit disconnect plug receptacles and a ground terminal, therein, said unit having in combination a plurality of connection plugs projecting in alignment therefromfor engaging with the disconnect receptacles upon a predetermined movement of the unit in the cubicle and having each plug provided with a stationary switch contact at the inner end thereof, a plurality of intermediate stationary switch contacts each hav- V ing a selective switch member pivotally mounted thereon and movable selectively into circuit closin engagement with either of a corresponding pair of the stationary switch contacts, means in cluding a removable operating handle having operative connection with the selective switch members only when the unit is outside the cubicle for operating the selective switch members to a selected position, and a plurality of grounding switch members having a common connection engageable with the ground terminal inside the cubicle and remotely releasable energy storing spring means having connections efiective only for operating the grounding switch members with a snap action into engagement with the corresponding intermediate stationary switch contacts for grounding the. same, latching means for independently holding the ground switch members in engagement with the intermediate switch con. tacts, and spring biasing means for operating the grounding switch members with a snap action out of engagement with the intermediate switch contacts upon release of the latching means.

8. A selective circuit grounding substitute unit for operation in a switchgear cubicle having sepa rate circuit disconnect plug receptacles and a ground terminal therein, said unit having in combination a plurality of connection plugs projecting in alignment therefrom for engaging with the disconnect receptacles upon a predetermined movement of the unit in the cubicle and having each plug provided with a stationary switch con tact at the inner end thereof, a plurality of in termediate stationary switch contacts each having a selective switch member pivotally mounted thereon and, movable selectively into circuit clos ing engagement with either of a corresponding pair of the stationary switch contacts, means in-- cluding a removable operating handle having operative connection with the selective switch members only when the unit is outside the cubicle for operating the selective switch members to a selected position, a plurality of grounding switch members having a common connection engageable with the ground terminal inside the cubicle, and an energy accumulating spring operating mechanism having a remotely operable releasing control element for jointly operating the grounding switch members with a snap action into circuit closing engagement with the intermediate stationary switch contacts for grounding the same, latching means for independently holding the grounding switch members in engagement with the intermediate stationary switch contacts, and spring biasing means for operating the grounding switch members with a snap action out of engagement with the intermediate stationary switch contacts upon release of the latching means.

9. A selective circuit grounding substitute unit having in combination a plurality of circuit connection plugs projecting in alignment therefrom and each provided with a stationary switch contact at the inner end thereof, a plurality of intermediate stationary switch contacts each having a switch member pivotally mounted thereon and movable selectively into circuit closing engagement with, either of a corresponding pair of the stationary switch contacts, a plurality of grounding switch members having a grounding connection and engageable with the intermediate stationary switch contacts for grounding the same, means including a spring charged mechanism having a remote electrically operable releasing element and a remote mechanically operable releasing element for jointly operatin the grounding switch members with a snap action into engagement with the intermediate stationary switch contacts for grounding the same, a holding latch for independently holding the grounding switch members in engagement with the intermediate stationary switch contacts and having a remote electrically operable releasing element and a remote mechanically operable releasing element, and spring biasing means for operating the grounding switch members with a snap action out of engagement with the intermediate stationary switch contacts upon release of the latch.

10. A selective circuit grounding unit havin in combination a plurality of circuit connection plugs projecting in alignment therefrom and each provided with a stationary switch contact at the inner end thereof, a plurality of intermediate stationary switch contacts each having a switch member pivotally mounted thereon and movable selectively into circuit closing engagement with either of a corresponding pair of the stationary switch contacts, a plurality of grounding switch members having a grounding connection and engageable with the intermediate stationary switch contacts for grounding the same, means including a spring charged mechanism having a remote electrically operable releasing element and a remote mechanically operable releasing element, for jointly operating the grounding switch members into engagement with the intermediate stationary contacts for grounding the same, a holding latch for independently holding the grounding switch members in engagement with the intermediate stationary switch contacts and having a remote electrically operable releasing element and a remote mechanically operable releasing element, and spring biasing means for operating the grounding switch members with a snap action out of engagement with the intermediate stationary switch contacts upon release of the latch, and selective interlocking means for rendering both the mechanically operable releasing elements and the electrically operable releasing elements effective or ineffective.

11. A selective circuit testing and grounding substitute unit for a drawout switchgear cubicle having inclosed circuit disconnect plug recep' tacles and a ground terminal inside thereof, said unit having in combination a plurality of connection plugs projecting therefrom for circuit closing engagement with the disconnect receptacles upon movement of the unit inside the cubicle and having each plug provided with a stationary switch contact at the inner end thereof, a plurality of test plug receptacles carried on the front of the unit and each having a circuit connection with a corresponding stationary switch contact, a plurality of intermediate insulated switch contacts mounted on the unit and each having a switch member pivotally mounted thereon and movable selectively into circuit closing engagement with either of a corresponding pair of the stationary switch contacts, selective operating means effective only when the unit is 5 unit inside a cubicle and provided with means for Jointly operating the grounding switch members into engagement with the intermediate switch contacts of the unit for grounding the same.

12. A selective circuit testing substitute unit for a drawout switchgear cubicle having a plurality of inclosed circuit disconnect plug receptacles, said unit having in combination a plurality of connection plugs projecting in alignment therefrom for circuit closing engagement with the disconnect receptacles upon movement of the unit inside the cubicle, a plurality of test plug receptacles carried in predetermined equally spaced-apart alignment on the front of the unit and each having a circuit connection with a corresponding connection plug, and a double pronged terminal testing device having the terminal prong spacing thereof corresponding to the spacing of said test receptacles for selectively interconnecting the testing device therebetween.

13. A selective circuit testing substitute unit for a drawout switchgear cubicle having inclosed circuit disconnect plug receptacles, said unit having in combination a plurality of connection plugs projecting in alignment therefrom for circuit closing engagement with the disconnect receptacles upon movement of the unit inside the cubicle, a plurality of test plug receptacles carried in predetermined equally spaced-apart alignment on the front of the unit and each having a circuit connection with a corresponding connection plug, and a double pronged terminal testing device having the terminal prong spacing thereof corresponding to the spacing of said test receptacles for selectively interconnecting the testing device therebetween, and provided with means for rotatably mounting one of the terminal prongs for movement to an inactive position.

HUGH KRIDA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,576,347 Mirrey Mar. 9, 1926 1,782,594 Allen Nov. 25, 1930 2,353,518 Specht July 11, 1944 2,504,775 Wood Apr. 18, 1950 FOREIGN PATENTS Number Country Date 387,384 Great Britain Feb. 6, 1938 

